The term “code” is meant to indicate any graphical representation that has the function of storing coded information. The term “coded information” is meant to indicate the set of identification data contained within a code, such as an optical code. The term “optical code” comprises graphical representations detectable both in the visible light field and in the range of wavelengths between infrared and ultraviolet.
Particular examples of an optical code consist in linear or two-dimensional codes, wherein information is encoded by using appropriate combinations of fixed-shape elements, for example square, rectangular or hexagonal, of a dark color (usually black) separated by light elements (spaces, usually white), such as bar codes, stacked codes and two-dimensional codes in general, color codes, etc. The term “optical code” also comprises, more generally, other graphical forms with an information coding function, including clearly printed characters (letters, numbers, etc.), special patterns (“pattern”) (such as stamps, logos, signatures, fingerprints, etc.) and optical information hidden by means of Digital Water Marking techniques.
The coded information can relate, for example, to distance, volume, size, identification data of an object and/or information relating to the object.
In the past, when there were only linear codes, optical code reading was usually performed by means of scanning an optical code using a beam of laser light emitted from a special laser reader or imager systems based on linear CCD sensors were used. With the advent of two-dimensional codes, the use of optical code readers of the imager type has become widespread, where the entire code, or the entire width of a linear code, is simultaneously illuminated and the light diffused by the entire illuminated optical code is collected and detected by a matrix type photo detector or image sensor. Imager type optical readers are typically equipped with an imager module (also called “imager engine” or “scan engine”), integrating a digital camera based on CCD or CMOS sensors.
The cameras are equipped with a lens system adapted to collect the light diffused by the optical code and convey it to the photo detector or image sensor, which converts the intensity thereof into an electrical signal. The image sensor is appropriately placed on the focal plane of the lens system, that is to say on the plane where the lens system is capable of reconstructing a focused image. The focal distance represents the distance from the lens system's optical center to the focal plane. In order to be able to clearly view an image, focusing is performed consisting in focusing the lens system at a suitable distance between the focal plane and the photographed object.
Optical code readers should be able to focus, that is, to adjust the distance between the lens system and the sensor to allow for the reading of optical codes at different distances. Such “dynamic” focus code readers are also known as autofocus readers.
The focus adjustment can be of an automatic or manual type. In either case, the focus adjustment system may comprise a lens system motion mechanism.
In the event of optical code readers with automatic focus adjustment, the motion mechanism typically comprises an electrical actuator. The drive of the electrical actuator can be controlled, during the normal operation of the optical code reader, based on the distance of the code to be read, automatically detected by the optical code reader by means of image analysis techniques or by a distance measuring instrument associated with the above reader.